1. Field of the Invention
The present general inventive concept relates to data processing, and more particularly to encoding and decoding methods to control a direct current (DC) component, and data processing apparatuses performing the encoding and decoding methods.
2. Description of the Related Art
Data information may be transmitted through a network, a microwave or a satellite transmission in a receivable form to a receiving apparatus. Also, the data information may be stored into standard storage media, such as a compact disc (CD), a digital video disc (DVD), a digital audio tape (DAT) and a hard disk.
Generally, the data is represented as digital data, and the digital data is rarely transmitted or stored in an original form. Instead, the data is compressed to reduce a size of the data or encoded to reduce data errors (e.g., channel encoding).
A compression performance is determined by a ratio of compressed digital data to original digital data, and a channel coding performance is determined by a size of redundant information and an error recovery ratio. The redundant information includes additional information lacking in the original digital data to recover the original digital data from the channel-coded data.
In an example of hard disk channel coding, recent hard disk coding methods are classified as either a modified frequency modulation (MFM) method or a run length limited (RLL) method. The RLL method has better compression performance and is safer than the MFM method.
The RLL method uses a code defining minimum and maximum distances of a transition between a bit ‘0’ and a bit ‘1’, and may add the redundant information in the original digital data due to limitations of the minimum and maximum distances. An RLL code generated by the RLL method is often referred to as a (d, k) code where d indicates the minimum distance and k indicates the maximum distance.
For example, the CD may have an 8/17 rate and adopt an eight-to-fourteen modulation (EFM) code, of which a minimum distance d is equal to 2 and a maximum distance k is equal to 10. The DVD may have an 8/16 rate and adopt an EFMPlus code, of which a minimum distance d is equal to 2 and a maximum distance k is equal to 10.
Also, storing methods of the hard disk may be classified as either a longitudinal magnetic recording (LMR) method or a perpendicular magnetic recording (PMR) method. The PMR method may store data 10 times more than the LMR method in the same storage media. However, the PMR method has a problem in that the digital data stored in the storage media is unstable when a direct current (DC) component is not properly controlled.
Nowadays, research is being conducted on using the RLL method and the PMR method to store the digital data.
A low-rate RLL method using a lot of the redundant information may properly control the DC component generated when the storage media such as the hard disk adopts the PMR method but may seriously reduce a storage density. Generally, the storage density of the storage media is an important factor and the low-rate RLL method may not be adequate.
A high-rate RLL method using only some of the redundant information may not significantly change the storage density but may not properly control the DC component that is generated when the storage media such as the hard disk adopts the PMR method. Generally, reliability of the digital data stored in the storage media is also an important factor and thus the high-rate RLL method may not be adequate if the DC component is not properly controlled.
Therefore, encoding and decoding methods capable of not significantly changing the storage density and properly controlling the DC component are required.